The present invention relates to a method for preparing light olefins such as ethylene and propylene through a naphtha and methanol mixed catalytic cracking reaction process involving a simultaneous cracking reaction of naphtha and methanol by using a circulating fluidized-bed reactor.
Light olefins such as ethylene and propylene are basic raw materials in the field of petrochemical industry and produced mostly from naphtha by high temperature pyrolysis process performed at over 800° C. At this time, the process is endothermic reaction, indicating the energy consumption is huge. Recently, according to the increase of natural gas cracker selectively producing ethylene, the competitiveness of naphtha cracker decreases. So, it is required to develop a novel method for producing olefins that can produce propylene selectively.
Recently, Korea Research Institute of Chemical Technology, SK Innovation, and KBR have developed ACO™ (Advanced Catalytic Olefins) process, the catalytic naphtha cracking process, that can increase the yield of propylene at least 100%, compared with the conventional pyrolysis process (Korean Patent No. 10-0651329 and Korean Patent No. 10-0632563).
In the meantime, MTO (Methanol to Olefin) technology has been introduced as a novel technology to prepare olefins, wherein methanol is produced from coal or natural gas through gasification or reforming and light olefins are produced from the obtained methanol above. The pyrolysis process of naphtha to produce light olefins is endothermic reaction, while MTO reaction to produce light olefins from methanol is exothermic reaction. So, during the reaction, a huge amount of heat is generated, which has to be eliminated. MTO process has been developed by UOP, USA, and DICP, China, etc, and is now in full operation for the industrial production of olefins.
As mentioned above, hydrocarbon cracking process is endothermic reaction and methanol cracking process is exothermic reaction. So, a coupling reaction of the two processes above is proposed for heat neutralization. According to Nowak et al., heat neutralization is possible if C4 hydrocarbon is added in the course of methanol conversion process (Appl. Catal. A, 50, (1989) 149-155). When methanol and n-butane are added at the ratio of 1:3 to the process, cracking reaction for the production of light olefins can be induced without additional energy supply or elimination.
However, methanol cracking process progresses faster than naphtha, the hydrocarbon, cracking process. Therefore, a simple coupling reaction of the two is disadvantage in increasing yield of light olefins due to the generation of many by-products.
Thus, the present inventors studied about naphtha and methanol mixed catalytic cracking reaction process involving a simultaneous cracking reaction of naphtha and methanol. In the course of the study, the inventors found out that the yield of light olefins could be increased by performing the naphtha and methanol cracking reaction simultaneously by using a circulating fluidized-bed reactor and by regulating the introduction positions of naphtha and methanol in the reactor, leading to the completion of the present invention.